Comprehensive, Consistent and Systematic Approach to the Mathematical Modeling of PEM Fuel Cells
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Polymer electrolyte membrane (PEM) fuel cells are a promising zero-emission power source for transportation applications. An important tool for advancing PEM fuel cell technology is mathematical modeling. Mathematical models can be used to provide insight on the physical phenomena occurring within a fuel cell, as well as aid in the design of fuel cells by simulating the effect of changes in design or operating conditions on performance. A comprehensive, consistent and systematic general formulation for a mathematical PEM fuel cell model is presented in this thesis. The formulation is developed by considering the fuel cell to be composed of several, co-existing phases. The conservation of mass, momentum, species, and energy are applied to each phase in the fuel cell. The interactions between the phases are modeled by applying a volume-averaging procedure to the conservation equations in each phase. The solution of the governing equations for the general formulation are beyond the scope of this thesis research. Instead, simplifying assumptions are applied to the general formulation in order to reduce the number of governing equations. The cell is assumed to be two-dimensional, steady state and isothermal. As well, the polymer electrolyte is assumed to be impervious to the gas phase and liquid water is assumed to exist only in the gas phase or polymer electrolyte. The numerical solution of the simplified formulation is implemented using the computer language of C++ and the finite volume method. The numerical solution provides details of the transport phenomena within the anode and cathode gas flow channels, electrode backing layers, and catalyst layers, as well as the polymer electrolyte membrane layer. These details include the bulk velocity of the gas phase; the concentrations of the species within the gas phase; the potential and current density in the solid phase and polymer electrolyte; the water content in the polymer electrolyte; and the distribution of reaction rate within the catalyst layers.